Method for separating oil from compressed gas

ABSTRACT

A refrigeration system is disclosed having a compressor of the screw type, and a stream of compressed gas and oil mist is used to cool the compressor and the motor. The oil is separated by passing the stream of refrigerant gas and oil through a unit which subjects the oil-laden gas to a thorough oil-separating treatment without restricting the flow of the oil-free gas.

United States Patent 1191 Soumerai et al. 145 Jan. 9, 1973 54] METHOD FOR SEPARATING OIL 58] Field of Search ..55/l83-188, 309, FROM COMPRESSED GAS 55/320, 321, 32s, 97, 337, 467-473; [75] Inventors: Henri Sournerai, West l-firtford; 62/470'473 Harold W. Moody, Jr., Farmington; Clark B. Hamilton, Wethersfield; [56] References cued B1311 cwemr)" UNITED STATES PATENTS r 3,085,381 4/1963 Sobeck ..55/473 [73] Ass'gnee' nunham'Bush west Hartford 3,291,385 12 1966 Williams et al ..55 473 Conn.

22 il d; July 9, 1971 Fr iinBrTEXHn iineF Bernard Wtfiidk AttorneyCurtis,Morris & Safford 21 Appl. No.2 161,275

[57] ABSTRACT Related Application Dam A refrigeration system is disclosed having a compres- |6()] Continuation-impart of Ser. No. 6l2,222, .Ian. 27, sor of the screw type and a strcam of cnmpressed gas 1967, Pat. N0. 3,408,826, which is a division 61 S61. and Oil mist is used to 9991 the compressor and the No. 666,372, Sept. 8, 1967, Pat. No. 3,408,828, and motor. The oil is separated by passing the stream of a Continuation of Oct 1968. refrigerant gas and oil through a unit which subjects the oil-laden gas to a thorough oil-separating treatment without restricting the flow of the oil-free gas. [52] US. Cl. ..55/97, 55/337, 55/473 H v [5 1] Int. Cl. ..B0ld 50/00 10 Claims, 3 Drawing Figures PATENTEDJAN ems 3.708.959 '1 INVENTORS Henri Soumerai Harold W. Moody, Jr. Clark B.Hcmilfon James R. Blofl 61.1.4, mm 4: Jjgnl ATTORNE METHOD FOR SEPARATING OIL FROM COMPRESSED GAS This application is a continuation-in-part of application Ser. No. 612,222, filed Jan. 27, 1967, now U.S. Pat. No. 3,408,826 issued Nov. 5, 1968, a division of Ser. No. 666,372 filed Sept. 8, 1967 now U.S. Pat. No. 3,408,828 issued Nov. 5, 1968 and a continuation of Ser. No. 810,410 filed Oct. 25, 1968 now abandoned, and covering the refrigeration system of the illustrative embodiment of the present invention.

The present invention is directed to the details of structure and mode of operation involved in the separation of the oil which is entrained in the stream of compressed refrigerant gas.

This invention relates to refrigeration, and more in particular to a refrigeration system and method wherein the compressor is of the screw type and the stream of compressed gas and oil passes through a special oil separator.

A11 object of this invention is to provide an improved refrigeration system of the type having a compressor from which a stream of compressed refrigerant gas contains oil which must be separated from the gas. Another object is to provide an improved method and means for separating oil from compressed gas. A further object is to provide for the above with compressors of the screw type. Another object is to provide means for maintaining desirable operating conditions in a screw compressor under varying loads and extreme conditions of use. A further object is to provide for the above in a manner which avoids the difficulties which have been encountered in the past with similar constructions. These and other objects will be in part obvious and in part pointed out below.

In the drawings:

FIG. 1 is a schematic representation of one embodiment of the invention;

FIG. 2 is a fragmentary perspective view of the oil separator unit of FIG. 1, with parts broken away; and

FIG. 3 is an enlarged view of the wire mesh which is in the oil separator unit of FIG. 1.

Referring to FIG. 1 of the drawings, a refrigeration system 2 includes: a screw compressor 4 having an unloader 5 and driven by an electric motor 6; an oil separator 8; a refrigerant discharge line 10; a watercooled condenser 12; a liquid refrigerant line 14 extending to a refrigerant control and restrictor assembly 112 from which the refrigerant flows to an evaporator 26; and, a gas refrigerant return line 32 through which the gas refrigerant returns to compressor 4.

The system also includes an oil circulating system including the following in series: an oil sump 34; an oil pump 36 driven by an electric motor 37; an oil cooler 38 through which water flows from a water inlet 40 to a water outlet 42 and which cools the oil flowing from the pump and, an oil filter 44. An oil supply line 46 delivers oil under controlled pressure through distributor lines 48 to the motor bearings 50 and through lines 52 and 54 and 56 to compressor 4. Oil is also delivered from line 46 through a line 58 to the unloader 5, and through a line 59 to a load control unit 60.

During operation, the dense high-pressure oil-gas mixture is discharged from compressor 4 into a chamber 62 and thence through the motor, whose housing defines a main flow path for the mixture, which mixture is discharged axially against a bafile 64. This gas-oil mixture uniformly blankets and cool the stator and rotor of the motor, and the motor also serves as a first-stage oil separator and removes, by centrifugal action, the bulk of the oil entrained in the gas. It has been found that something of the order of 95 percent of the oil is removed by the motor, and the oil accumulates at 66 in the bottom of the housing from which it flows through a line 35 to oil sump 34. The remaining fine oil mist is then separated from the gas by the action of baffle 64 and oil separator 8.

The disk-like baffle 64 deflects the stream of gas radially outwardly toward the outer wall and the oil then flows axially past the edge of the baffle through an annular passageway 68. Positioned in axial alignment with passageway 68 is an annular separator unit 70 which effectively removes the oil from the gas passing through it. Separator unit 70 includes (see also FIG. 2) a loosely-formed ring or annular separator 71 of knitted wire mesh which is wound upon a perforated tubular mandril 72. Mandril 72 forms a central gas discharge passageway 74 through which the gas flows to a gas discharge tube 73 and thence past a check valve 75 to line 10.

Separator 71 is in the form of two rolls 77 and 79, each of which is formed by a two-ply strip 81 (see FIG. 3) of knitted wire mesh. Roll 79 is twice the axial dimension of roll 77, and is formed by two strips 81 side-by-side. In this embodiment strip 81 is illustratively 7 inches wide and is formed by first knitting a wiremesh tube having 60 openings per square inch and using steel wire or .011 inch in diameter. The mesh tube is then flattened to form the two-ply strip 81, and it is crimped diagonally of the strip to form ridges, with the crimping being 1/4 inch deep, and with the ridges being nine thirty-seconds inch wide from ridge to ridge. A strip 81 is wound loosely on mandril 72 to form roll 77, and two strips 81 are wound loosely side-by-side to form roll 79. A perforated support plate is assembled on mandril 72 at the side of roll 77. The radius of roll 77 is less than that of roll 79, so that there is an annular passageway 83 between roll 77 and shell 61. Illustratively, the radius of the inner surface of shell 61 is of the order of 10 inches, and the radius of roll 77 is 8% inches. Therefore, a portion of the annular stream of gas with entrained oil flowing axially from passageway 68 may continue its axial flow through the perforations in plate 85 and along passageway 83.

The portion of the stream adjacent the periphery of baffle 64 impinges against plate 85 at the periphery of roll 77, and may pass through the perforations in the plate and into the roll. However, support plate 85 is spaced axially from baffle 64, so as to provide a radial passageway or free flow path 76 through which the gas may flow radially inwardly from the main flow path to passageway 74, without passing through separator 71. Therefore, it might be expected that some of the gas with entrained oil will pass radially inwardly through passageway 76 and enter passageway 74 without giving up its oil. However, it has been found that with the arrangement herein disclosed, there is a tendency for two-phase fluid flow axially through passageway 76 with gas having the oil mist therein flowing along the casing wall and through the perforations in plate 85 and along passageway 83, while oil-free gas flows adjacent bafile 64 and thence radially inwardly through passageway 76. The oil-laden gas in passageway 83 impinges against the rolls 77 and 79, and there is a very substantial increase in the cross-sectional area of the flow path which causes a substantial reduction in the rate of flow. Hence, from passageway 83 the gas flows or migrates radially inwardly at a very slow flow rate toward the centratmandril 72. Mandril 72 and plate 85 are sheet metal of sufficient rigidity to provide the desired support, and yet the perforations are of sufficient size and number to permit the relatively free flow of the gas through the plate and through the mandril wall. Hence, at the outer periphery of roll 77, some of the gas passes through plate 85 directly into roll 77.

During the flow through rolls 77 and 79, the oil adheres to the exposed surfaces of the wire mesh and flows downwardly and collects at the bottom of the easing 61 in the body of oil 66. There may be a tendency for the oil to bridge some of the passageways or perforations between the adjacent portions of the wire mesh in rolls. 77 and 79. Such bridging of the passageways could be expected to cause the oil to be re-entrained in the gas so as to reduce the effectiveness of the. oil separator. However, such re-entrainment does not occur, apparently because of the reduced fluid flow causes an increased amount of the refrigerant gas to be free of oil and to pass radially inwardly through passageway 68 without passing through rolls 77 and 79.,

Certain details of the construction of the illustrative embodime ntare set forth above, and it has been explained that very satisfactory results are obtained withinthe full range of variations in load on the compressor. In general the winding tension on the wire mesh must not be high enough to prevent the free flow of the refrigerant gas at a slow rate toward the central passageway 74 formed by mandril 72. In the illustrative embodiment mandril '72 has a diameter of the order of 7 inches, and baffle 64 has a diameter of 14 inches and is spaced 1% inches from plate 85. The wire mesh forming rolls 77 and 79 is of substantially uniform density of the order of 15.5 poundsper cubic foot. It must be understood that these specific dimensions and other physical characteristics are illustrative.

As indicated above, unloader controls the operation of the compressor so that it compresses the amount of refrigerant required for the load at all times. Accordingly, compressor 4 has a capacity control slide valve 120 which is shown in the full-load position wherein it formsa portion of the compressor-rotor casing 122. Slide valve 120 is mounted to slide to the left from the position shown to thereby expose an opening in the bottom of the rotor casing through which the suction gas can pass back from the central portion of the compressor to the suction inlet. in this way the amount of gas pumped is reduced.

Sliding valve 120 is connected through an operated spindle 124 to a piston 126 which is slidable in a cylinder 128. Piston 126 is moved to the left from the position shown by supplying oil at a controlled pressure to the chamber 130 in the cylinder at the right of the a piston. Cylinder 128 is open at its left-hand end to the suction pressure of the compressor. Hence, when oil is supplied to chamber 130 at a pressure greater than the discharge pressure, piston 126 is moved to the left; and, when the pressure of the oil in chamber 130 is less than the discharge pressure, piston 126 moves to the right. Oil supply line 58 is connected to chamber 130 through a shut-off valve 132 and a line 134. Hence, when valve 132 is open the oil at the full pressure in lines 46 and 58 is supplied at once to chamber 130. Also, a flow circuit is provided in parallel with valve 132 by line 59 and a restrictor valve 136 and a shut-off valve 138. Hence, when valve 132 is closed and valve 138 is opened, the oil at the pressure of line 46 flows throughline 59, restrictor 136, valve 138 and line 134 to chamber 130. However, restrictor 136 limits the rate of flow so that piston 126 is moved at a reduced by controlled rate, whereas when valve 132 is open the piston moves at a rapid rate. This permits unloading rapidly by opening valve l32,or unloading at a slower rate by opening valve 138.

An additional control circuit is provided by a shut-off valve 140 and a restrictor 142 in a line 144 which extends between the suction inlet of the compressor housing and chamber 130. Hence, when valve 140 is open the oil in chamber 130 is free to flow through line 134, restrictor 142, line 144, and valve 140 to the compressor casing. As indicated above, when the compressor is operating, the pressure of the compressed gas at the discharge side of the compressor urges sliding valve toward its full-load position. Hence, when valve 140 is open, the pressure equalizes on the two sides of the piston because of the flow of oil from chamber 130, and the discharge pressure acting on slide valve 120 moves the slide and piston 126 back to the position shown. Restrictor 142 controls the rate of flow of oil from chamber and therefore controls the rate of movement of the piston from a partial-load position to the full-load position.

The oil pressure in line 46 is controlled by a control unit 146 which has a valve 148 in a line 150 extending from line 46 to sump 34. A control line 152 extends from unit 146 to the discharge chamber 62 of the compressor so that unit 146 is responsive to the compressor discharge pressure. Unit 146 and its valve 148 act as a relief valve to maintain a pressure in line 46 which is a predetermined amount above thepressure in chamber 62. lllustratively, when the compressed gas pressure in chamber 62 is 200 pounds per square inch, the pressure in line 46 is 240 pounds per square inch. Hence, the oil delivered. to the compressor through the various lines 48, 52, 54 and 56, and through lines 58 and 59 to the unloader is maintained at a predetermined value above the compressor discharge pressure. This insures a proper and adequate supply of oil to the motor bearingsand to the compressor. It also insures that the unloader will operate properly. The opening of valve 132 whenv the compressor is partially or fully loaded will unload it at a rapid rate. The opening of valve when the compressor ispartially or completely unloaded will fully load it at a controlled rate.

It has been pointed out above that the heavy mixture of compressed gas and oil mist provides a very satisfactory cooling of the motor. The oil mist produces a scrubbing action which improves the heat exchange factor and increases the cooling of the motor. The oil which is supplied to the compressor may contain some refrigerant and that refrigerant tends to flash and to aid in the cooling effect of the oil. It is thus seen that the refrigerant and the oil are circulated through separate cycles, but that inter-relationship is maintained which provides an improved mode of operation. Pump 36 is started prior to the starting of motor 6 so that the oil pressure builds up and provides oil for the motor and compressor, and the desired oil pressure is provided for the unloader. The controls also provide automatic unloading at start-up.

The system of FIG. 1 includes standard components and controls. It is also understood that the embodiment herein disclosed is illustrative, and it is contemplated that changes and modifications may be made within the scope of the invention. Reference may be had to the above-identified co-pending application, which is incorporated herein by reference.

What is claimed is:

1. In the art of separating oil from compressed gas with the separation taking place between a receiving zone and a discharge zone, the steps of, flowing the gas from said receiving zone to produce a two phase fluid flow in a stream having different concentrations of the phases in the cross-section thereof, at one side of which there is substantially oil-free gas and at the other side of which there is oil-laden gas, passing the substantially oil-free gas from one side of said stream along a substantially unobstructed path to an outlet in said discharge zone, separating oil from said oil-laden gas to thereby form a second stream of substantially oil-free gas by passing said oil-laden gas from said other side of said stream through an oil separating zone to said discharge zone, said oil separating zone having a great multiplicity of circuitous flow paths of small cross-section defined by exposed surfaces to which the oil adheres and from which the oil is collected, said circuitous flow paths providing random flow for the gas with the equivalent of a passageway which increases in cross-section downstream whereby the flow rate of the gas in the random streams is materially reduced so as to avoid the re-entrainment of oil from said surfaces into the gas, draining the oil from said surfaces, combining said streams of substantially oil-free gas, and removing said combined streams of substantially oil free gas through said discharge zone outlet.

2. A method as in claim 1 which includes the initial step of producing a gas stream with an annular flow of gas, and said step of passing said oil-free gas stream comprises the step of flowing the oil-free gas stream radially inwardly of said oil entraining gas stream.

3. The method as described in claim 1 wherein said gas enters said receiving zone in a stream which has a central axis, and which includes the initial step of deflecting the stream radially outwardly by baffle 1 means.

5. The method as described in claim 1 which includes the initial step of deflecting the flow of gas to change the general direction of the flow substantially 90 and thence substantially back to the original general direction of flow and thereby direct the oil-laden gas toward said separating zone.

6. The method as described in claim 5 wherein said discharge zone comprises an unobstructed passageway which extends in the direction of the original flow of the compressed gas from said receiving zone.

7. A method of separating oil from compressed gas comprising the steps of, producing two-phase liquid flow in a stream having different concentrations of the phases in the cross-section thereof, at one side of which there is substantially oil-free gas and at the other side of which there is oil-laden gas, separating said oil-free gas from said oil-laden gas to produce separate streams, directing said oil-free gas stream along a substantially unobstructed path to an outlet of a discharge zone, separately directing said oil-laden gas stream to said discharge zone outlet through an oil separating zone having substantially increasing cross-section and divided into a multiplicity of circuitous flow paths with a body of mesh having random shaped passages, separating the oil from the gas in said oil-laden gas stream in said separating zone to produce a second oil-free gas stream, directing said second oil-free gas stream from said separating zone to said discharge zone, and joining said second oil-free gas stream with the first mentioned oil-free gas stream in said discharge zone for simultaneous discharge through said outlet.

8. A method as in claim 7 including the steps of providing a substantial number of surfaces in said separating zone upon which said oil collects and removing said oil from said zone by the aid of gravity.

9. A method as in claim 7 which includes the step of bypassing said separating zone with said first mentioned oil-free gas stream which comprises the step of changing the direction of flow of said first mentioned oil-free gas stream with respect to said oil-laden gas stream.

10. A method as in claim 7 wherein said step of producing a two phase flow of gas and oil mist includes the stem of directing said oil-laden gas stream along an annular flow path, and said step of separating said first mentioned oil-free gas stream from said oil-laden gas stream comprises the step of flowing said first mentioned oil-free gas stream radially inwardly of said oilladen gas stream and towards said discharge zone.

l i I! t i 

2. A method as in claim 1 which includes the initial step of producing a gas stream with an annular flow of gas, and said step of passing said oil-free gas stream comprises the step of flowing the oil-free gas stream radially inwardly of said oil entraining gas stream.
 3. The method as described in claim 1 wherein said circuitous flow paths and said surfaces are formed by providing a body of mesh.
 4. The method as described in claim 3 wherein the gas enters said receiving zone in a stream which has a central axis, and which includes the initial step of deflecting the stream radially outwardly by baffle means.
 5. The method as described in claim 1 which includes the initial step of deflecting the flow of gas to change the general direction of the flow substantially 90* and thence substantially back to the original general direction of flow and thereby direct the oil-laden gas toward said separating zone.
 6. The method as described in claim 5 wherein said discharge zone comprises an unobstructed passageway which extends in the direction of the original flow of the compressed gas from said receiving zone.
 7. A method of separating oil from compressed gas comprising the steps of, producing two-phase liquid flow in a stream having different concentrations of the phases in the cross-section thereof, at one side of which there is substantially oil-free gas and at the other side of which there is oil-laden gas, separating said oil-free gas from said oil-laden gas to produce separate streams, directing said oil-free gas stream along a substantially unobstructed path to an outlet of a discharge zone, separately directing said oil-laden gas stream to said discharge zone outlet through an oil separating zone having substantially increasing cross-section and divided into a multiplicity of circuitous flow paths with a body of mesh having random shaped passages, separating the oil from the gas in said oil-laden gas stream in said separating zone to produce a second oil-free gas stream, directing said second oil-free gas stream from said separating zone to said discharge zone, and joining said second oil-free gas stream with the first mentioned oil-free gas stream in said discharge zone for simultaneous discharge through said outlet.
 8. A method as in claim 7 including the steps of providing a substantial number of surfaces in said separating zone upon which said oil collects and removing said oil from said zone by the aid of gravity.
 9. A method as in claim 7 which includes the step of bypassing said separating zone with said first mentioned oil-free gas stream which comprises the step of changing the direction of flow of said first mentioned oil-free gas stream with respect to said oil-laden gas stream.
 10. A method as in claim 7 wherein said step of producing a two phase flow of gas and oil mist includes the stem of directing said oil-laden gas stream along an annular flow path, and said step of separating said first mentioned oil-free gas stream from said oil-laden gas stream comprises the step of flowing said first mentioned oil-free gas stream radially inwardly of said oil-laden gas stream and towards said discharge zone. 